Seamless alum. gutters were installed maybe 17 years ago on my little
brick bungalow in midwest US.

"Seamless" on the straight lengths. The corner pieces were sealed
with something that looks like caulk inside the gutter.

I noticed one corner leaking the other day. Exactly where it does
the 90 degree turn.

What should I use to re-seal inside the corners? 100% silicone caulk?
Maybe DAP (I won't touch GE)??

Thanks,
Peetie